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- SQL.How can you compare two nullable values safely, and how does IS DISTINCT FROM differ from <>?
- SQL.How are NULL values ordered by ORDER BY, how do defaults differ between databases, and how can you control their placement?
- SQL.How does NULL propagate through arithmetic expressions, and how can COALESCE and NULLIF help handle missing values and division by zero?
- SQL.How does NULL affect join conditions, and why can filtering the right-hand table in WHERE remove unmatched rows from a LEFT JOIN?
- SQL.How do GROUP BY and DISTINCT treat NULL values, even though NULL = NULL evaluates to UNKNOWN?
- SQL.How do aggregate functions handle NULL, and what is the difference between COUNT(*), COUNT(column), and COUNT(DISTINCT column)?
- SQL.How does NULL affect IN and NOT IN, and why can NOT EXISTS be a safer choice when a subquery returns nullable values?
- SQL.How do WHERE, HAVING, and CHECK constraints treat conditions that evaluate to UNKNOWN?
- SQL.Why do column = NULL and column <> NULL not work as expected, and when should you use IS NULL and IS NOT NULL?
- SQL.What is SQL’s three-valued logic (TRUE, FALSE, UNKNOWN), and how do AND, OR, and NOT behave with UNKNOWN?
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- SQL.What are domain types (or constraints on data types), and how do they help enforce data correctness?
- SQL.How does SQL handle comparisons between different data types (for example, string vs number), and why is this dangerous?
- SQL.What is the difference between DATE, TIME, TIMESTAMP, and TIMESTAMPTZ, and which one should be used for business events?
- SQL.How do numeric types like INTEGER, BIGINT, DECIMAL, and FLOAT differ in terms of precision and use cases?
- SQL.What problems can arise from implicit type casting in SQL, and how can it affect indexes?
- SQL.How does NULL differ from 0, an empty string, or FALSE in SQL?
- SQL.What is the difference between CHAR, VARCHAR, and TEXT, and when would you choose each?
- SQL.What is MVCC ?
- SQL.What is AutoVacuum Postgres ?
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Category Archives: Без рубрики
Java.DBMigrationTools.What is a Flyway baseline?
A Flyway baseline tells Flyway: “Start tracking from this version — assume all migrations before this are already applied.” It lets you start using Flyway with an existing database without re-running old scripts. 🔍 Detailed Explanation Imagine you have a … Continue reading
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Java.DBMigrationTools.Can you use Java code to write Flyway migrations?
✅ Short Answer Yes, you can write migrations in Java by implementing the JavaMigration interface or extending BaseJavaMigration.This allows you to write complex, logic-driven database changes in code, including loops, conditional logic, or calling other APIs. 🔍 How to Write … Continue reading
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Java.DBMigrationTools.What is flyway.migrate() used for?
**flyway.migrate()** is the core method in Flyway used to apply pending migrations to your database. It scans the migration files, checks which ones haven’t been applied (based on flyway_schema_history), and executes them in order. 🧠 When Would You Use It? … Continue reading
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Java.DBMigrationTools.What happens if you rename a Flyway migration file?
If you rename a Flyway migration file that was already executed, Flyway will treat it as a new migration and might: ❌ Try to re-run it (if version number changes) ❌ Throw a checksum error (if only filename changes) ✅ … Continue reading
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Java.DBMigrationTools.What’s the difference between versioned and repeatable migrations?
Versioned migrations run once, in a strict order, and never again. Repeatable migrations can run multiple times — they’re re-applied whenever the file changes. They serve different purposes in managing your database schema. 🔍 Detailed Comparison Feature Versioned Migrations Repeatable … Continue reading
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Java.DBMigrationTools.What is the flyway_schema_history table?
The flyway_schema_history table is a metadata table automatically created by Flyway in your database.It records which migrations have been applied, in what order, by whom, and when — ensuring each migration is executed exactly once. 🔎 Detailed Explanation When you … Continue reading
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Java.DBMigrationTools.What naming convention does Flyway use for migration files?
Flyway uses a structured naming convention for migration files: ✅ The V stands for versioned migration✅ A double underscore __ separates the version from the description✅ The description is free-form (no spaces) and helps identify the purpose✅ The file must … Continue reading
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Java.DBMigrationTools.What is Flyway?
Flyway is a lightweight, Java-based database migration tool that helps you version, manage, and automate schema changes using plain SQL or Java migration scripts. It’s simple, fast, and widely used in microservices, CI/CD pipelines, and Spring Boot projects. 🔎 Detailed … Continue reading
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Java.DBMigrationTools.What is a logicalFilePath?
✅ Short Answer The logicalFilePath is an identifier for a changelog file that Liquibase uses internally to track changesets — instead of the physical file path. It helps ensure consistent tracking of changesets even if the file is moved, renamed, … Continue reading
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Java.DBMigrationTools.What is the purpose of include and includeAll in changelogs?
✅ Short Answer **<include>** lets you include one specific changelog file into another **<includeAll>** lets you include all changelogs from a folder, automatically This helps you modularize and organize your migrations across many files.. 🔎 Detailed Explanation 🔹 include Used … Continue reading
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